The complete or partial detachment of ligaments, tendons or other soft tissues from their associated bones within the body is a relatively common injury, particularly among athletes. Such injuries generally result from excessive stresses being placed on these soft tissues. For example, a tissue-detaching injury may occur as the result of an accident such as a fall, overexertion during a work-related activity, during the course of an athletic event, or in any one of many other situations and/or activities.
In the case of a partial detachment, commonly referred to under the general term “sprain,” the injury will frequently heal itself, if given sufficient time, and if care is taken not to expose the injury to any undue or extraordinary stress during the healing process. If, however, the ligament or tendon is completely detached from its associated bone or bones, or if it is severed as the result of a traumatic injury, partial or permanent disability may result. Fortunately, a number of surgical techniques exist for re-attaching such detached tissues and/or completely replacing severely damaged tissues.
One such technique involves the replacement of the detached tissue using autogeneic tissue grafts harvested from elsewhere in the body. For example, an anterior cruciate ligament in a human knee can be replaced and/or repaired using a patellar tendon autograft or hamstring tendons. The patellar tendon is harvested with a bone block from the tibia, using the center third of the patellar tendon, and bone block from the patella. This graft has the advantage of having high initial strength and having bone plugs that will facilitate fixation. These grafts are implanted by forming bone tunnels through the tibia and/or femur at the points of normal attachment of the anterior cruciate ligament. A patellar tendon graft, with a bone plug on each of its ends, is harvested and sized to fit within the bone tunnels. Suture is then attached to the outer end of each bone plug, and thereafter passed through the femoral and/or tibial bone tunnels. The femoral plug and the tibial plug are then inserted into the appropriate bone tunnel behind the suture. Subsequently, the suture is drawn tight to position the bone plugs in the desired location, and impart the desired degree of tension to the ligament graft. Finally, while holding the bone plugs in position, interference screws, cross-pins or other fixation devices are used to securely lock the bone plug in position. The hamstring tendon grafts are implanted in a similar fashion.
While autogeneic tissue grafts have been successfully used to replace connective tissue, the harvesting procedure, like any medical procedure, has associated risks. Two primary concerns are tissue damage at the harvest site during the removal process and donor site morbidity. Complications in harvest have sometimes resulted in patellar fracture. In other cases, patellofemoral pain is observed due to donor site morbidity. Yet, even when the harvesting procedure is successfully performed, the sample may not provide a sufficient supply of tissue for a graft and/or the tissue may not have the desired quality or consistency. In addition, even with a successful surgery, it is possible for patients to rerupture the graft and require revision surgery. For these reasons, there is a need for an alternative source for tissue grafts, which can provide the properties of an autogenic tissue graft.
One example of an alternative graft is allograft tissue. The advantages of using an allograft include elimination of donor site morbidity and decrease in operating time. However, the graft has potential ability to transmit disease and elicit an immune response. There is also a lack of consistency in mechanical properties of the graft and the supply is limited.
For these reasons, there is a need to develop a connective tissue graft that is terminally sterilized and made from synthetic materials or biologically-derived materials. In the past, the initial results using synthetic prosthetic ligament devices looked promising. However, the long term results, such as those that extend beyond one year, showed the mechanical failure of the these devices. These prostheses have been found to lack sufficient strength and durability to act as a permanent replacement for the lifetime of the patient. Other prostheses, such as some made from synthetic materials, have good physical properties, but can erode or cause bone erosion.
Despite existing technology and techniques, there remains a need for connective tissue implants that can provide an approximation of the natural tissue to be replaced or augmented.